Production of photographic silver images by physical development



United States Patent 3,149,970 PRDDUQTIQN 0F PHOTQGRAPHKCSILVER EMAGESBY PHYSICAL DEVELOPMENT Edith Weyde, Leverlrusen, Germany, assignor toAGFA Alrtiengeseilsehaft, Leverhusen, Germany, a corporation of GermanyNo Drawing. Filed Jan. 5, 1966, Ser. No. 513 Claims priority,application Germany Jan. 10, 1959 7 Claims. (Cl. 96-48) The presentinvention relates to the production of photographic silver images byphysical development maliing use of light-sensitive layers having a lowcontent of silver halide or colloidal silver.

It is known that photographic silver images can be pro duced by means ofa physical developer. This physical developer contains in principledissolved silver salts as Well as silver halide developing agents. Forproducing the silver images ordinary photographic silver halide emulsionlayers are used which, after exposure, are first fixed and thendeveloped in said physical developer. This process is seldom used inpractice on account of the loss in lightsensitivity connected therewith,the comparatively long processing time required, and the low density ofthe silver image obtained therewith.

It has now been found that these draw-backs connected with theproduction of photographic silver images by means of a physicaldeveloper can be overcome if silver halide emulsion layers are usedwhich have a very low content of silver halide, and if these layers,after exposure, are subjected to a physical development without previousfixing.

For the production of the aforementioned silver halide emulsion layersthere are preferably used silver halide emulsions which contain perliter silver halide in an amount corresponding to about 0.1-1 g. ofsilver. The process can, however, also be carried out with a silverhalide emulsion containing 0.01 to 3 g. of silver in the form of silverhalide per liter of emulsion. Even emulsions with only one mg. of silverchloride or silver bromide per liter of 6 percent gelatin solution stillproduce an image, even though this image is of low quality. The use ofemulsions with more than 1 g. of silver per liter, generally does notproduce any appreciable improvement in the light-sensitivity. The silverhalide of these emulsions may consist of silver chloride, silverbromide, or mixtures of silver chloride and silver bromide in anyproportions. Moreover, silver iodide may be present in these emulsions,preferably in an amount up to 10 percent by Weight as calculated on thetotal amount of silver halide. The binding agent of the silver halideemulsion preferably consists of gelatin which may be present in anamount of about 1 to 10 percent, preferably 4 to 8 percent.

It has, furthermore, been found that such silver halide emulsions areespecially effective for the production of which the precipitation ofthe silver halide is effected without using a large excess of halogensalts so that these emulsions are not consequently subjected to anOstwald ripening (which refers to enlargement of the silver halide grainor crystal, and is different from chemical or afterripening).Furthermore, it has been found advantageous to so adjust theconcentrations of the solutions used for the production of the silverhalide emulsions that the emulsions obtained need not be substantiallydiluted in order to obtain the aforementioned concentrations. For theprecipitation of the silver halide there may be used silver nitrate orany other Water-soluble silver salts on the one hand and alkali-metaland halide such as sodium chloride, potassium bromide, potassium iodideon the other hand. The water-soluble silver salts and the alkali-metalhalides are preferably used in equivalent amounts. It is, hoW- ever,also possible to use the alkali-metal halides in a stoichiometricalexcess up to about percent since in the latter case Ostwald-ripeningusually does not occur due to the small concentrations of the halogensalts used. In any case, the concentration of the halogen salts shouldbe so small at the time of precipitation that the solubility .of thesilver halide is insignificant so that no or practically no enlargementof the silver halide grain occurs during the production and during theWorking-up of the emulsions. For example, if a relatively large excessof sodium chloride is added to an emulsion of the above type, and if theemulsion is allowed to digest for some hours at elevated temperature,and enlargement of the grain occurs, Whereby the production of the imagein the manner previously described is less satisfactory.

These emulsions precipitated in very dilute form have, as expected, avery low light-sensitivity. It has however been found that suchemulsions can be sensitized with sensitizing dyes on a quite unusuallyhigh scale, the sensitization being comparatively stronger the smallerthe amount of silver that is contained in the emulsions. It wasestablished that all known sensitizing dyes produce the eifect. If thereare simultaneously used different dyes which sensitize the emulsion fordifferent spectral regions, then layers can be obtained which have asubstantially higher sensitivity than for example that of emulsions formicro-films, which are comparable with these emulsions as regards grainsize. Suitable optical sensitizers are for instance those which aredisclosed in German Patents Nos. 733,026; 725,825; 737,639; 730,852;714,764; 757,784; 888,046; 927,527 and 929,080 and US. Patents Nos.2,226,156; 2,231,659; 2,185,182. and British Patents Nos. 466,244;493,455; 519,895 and 509,927. Moreover there may be further cited by Wayof example eosin, erythrosin, pinacyanol.

The type of gelatin which is used also has a strong influence on thesensitivity of such emulsions. Even extremely small quantities ofripening substances are sufiicicut to improve the sensitivity, while onthe other hand inhibiting substances can greatly reduce the sensitivity.

Binding agents other than gelatin, for example polyvinyl alco-hol andits derivatives, carboxymethyl cellulose and the like, also producelayers which are suitable for use.

The layers, after imagewise exposure, can be processed in various ways.For example the exposed silver halide layer may be brought into contactwith an unexposed silver chloride layer in the presence of a silverhalide developer solution, containing a silver halide solvent, and thiscan for example take place in an apparatus which is used for the silversalt diffusion process as it is for instance disclosed in French PatentNo. 879,995 or in British Patent No. 672,844, U. S. Patent No. 2,657,618or French Patent No. 1,015,772. In this case the auxiliary silverchloride layer serves as a silver donor, since silver chloride isdissolved by the developer solution containing a silver halide solventand thereafter is brought into contact with the exposed silver halidelayer. Instead of a silver chloride layer there may also be used asilver chlorobromide layer, the silver halide of which con tains up toabout 30 percent of silver bromide. A few seconds after the two layershave entered into contact, they can be separated from one another and anegative silver image of the copied original is seen in the exposedlayer. This only has to be rinsed for a short time before being dried,fixing being unnecessary.

The processing can however also be carried out With a physical developerwhich contains silver salts as well as reducing agents, but then alonger time is required for the production of the image. The image isvery rapidly obtained if the exposed layer is first treated with anaqueous solution of a silver salt in the form of a complex compound withfor example a sulphite or a thiosulphate and then with a silver halidedeveloper solution. The following method has also proved verysatisfactory: Silver halide developer substances which are resistant todiffusion, for example those indicated in German Patent No. 954,391, areadded to the silver halide layer. After exposure of such layers, theyare treated with an alkaline aqueous solution of a silver complex salt,as for instance the complex salt of silver chloride and sodiumthiosulfate, and since no developer substances can enter the solution ofthe silver salts, these solutions remain essentially unchanged incomposition and can be reused frequently.

It is, furthermore, possible to use a two-layer system, in which casethere is for example employed, as silver donor, a normal silver chloridelayer which must not contain any water-soluble silver halide salts andwhich is only sensitive to blue light. As light-sensitive layer, thereis used a silver halide layer with a low silver content as disclosedabove, which layer has for example been sensitized for green light.After exposure behind 'a yellow filter, the processing is carried outwith a silver halide developer solution which contains the silver halidesolvent. The silver chloride of the auxiliary layer is dissolved,diffuses into the layer with a low silver content and is depositedtherein on the nuclei which are formed by exposure to light. The silverchloride auxiliary layer can also have added thereto dyes which serve asantihalation layer and which are bleached in the processing. Theauxiliary layer is preferably arranged as the outer layer; however, itmay also form the inner layer. After processing the auxiliary layer neednot be removed from the image layer, since the silver chloride of theauxiliary layer is usually completely dissolved in the developingsolution. The layers with low silver content can also be coated with aprotective layer, this producing the advantage of better whites.

In order to obtain black silver deposits, it is advisable to addstabilizers or toning agents such as heterocyclic nitrogen-sulphurcompounds, for example -phenyl-n1ercapto-tetrazole in ordinaryconcentrations, either to the processing bath, to the layer having a lowsilver content, or to the silver chloride auxiliary layer. Thesesubstances somewhat delay the silver deposition owing to the sparingsolubility of their silver salts in silver halide solvents.

Light dispersion plays no part in these layers having a low silvercontent, since these layers are completely clear and transparent, andthe resolving power is thus extremely high. Moreover, since the imagesilver which forms during the processing and which precipitates from thesolution is of very fine grain, such images can be very greatlyenlarged.

It hasbeen found possible using such layers with a low silver content incombination with the present developing method also to produce directpositive images by using the Herschel effect, for example in accordancewith British Patent No. 748,681. It is known that silver halide emulsionlayers, especially silver chloride emulsion layers, which are foggedeither by light or chemical means, can be so modified by additives suchas pinacryptol yellow or those disclosed in British Patents Nos. 748,681and 667,206 that, when they are exposed to rays of relatively long wavelength (yellow or red), they produce a positive image after development,because the light of longer wave length has made the fogging nucleiineffective. It has now been found that the same effect is produced byusing, instead of an ordinary fogged silver halide emulsion, sil vernuclei which have been prepared from the emulsions of the presentinvention, especially silver chloride emulsion, or from dilute solutionsof water-soluble silver salts such as silver nitrate, which solutionscontain gelatin or other suitable binding agents in an amount of about 2to percent by weight. The last mentioned solutions preferably contain0.001 to l g. of silver per liter. Here also, the best results areobtained by using layers which contain l 0.001 to 0.1 g. of silver incolloidal form per square meter of surface area, which is equivalent tofrom 0.0001 to 0.01 milligram per square centimeter.

These materials are provided with the same additives as those used forthe direct positive emulsions based on the Herschel effect such as (l)2-(2,4dinitrostyryl)benzothiazole and similar heterocyclic compounds ofthe benzothiazole, quinoline, indolenine, benzotriazole, and rhodanineseries, the fused phenyl radicals of which are substituted by at leastone nitro radical and their alkyl quaternary salts, such as aredescribed in British Patent No. 667,206, and (2) o-nitrobenzylpyridiniumchloride and similar six-numbered heterocyclic compounds containing aring nitrogen atom and a nitrobenzyl substituent radical, such as aredescribed in British Patent No. 748,681, these additives beingpreferably used in amounts of 0.1 to 10 g. per liter of emulsion. At theexposed areas, the silver nuclei are made ineffective by thesesubstances and a positive silver image is obtained after processing byone of the methods described above.

Example 1 To a 6 percent aqueous gelatin solution at a temperature of 40C. are added per liter, 1 cc. of a 1 percent sodium chloride solution, 3cc. of a 1 percent silver nitrate solution and 1 cc. of a 0.01 percenteosin solution, from which a photographic layer is cast onto a paper orfilm support. The thickness of the dried layer will be between 2 and 10microns.

After exposure to an original by means of an incandescent lamp thislayer is conducted through an apparatus such as that used for the silversalt diffusion process, and an ordinary unexposed silver chloride layeris used as the silver donor. The developer solution applied has thefollowing composition:

1000 cc. of water 15 g. of hydroquinone l g. of 2-phenyl-3-pyrazolidone10 g. of caustic soda 40 g. of anhydrous sodium sulphite 1 g. ofpotassium bromide 15 g. of sodium thiosulphate 0.01 g. of5-phenylmercaptotetrazole Shortly after the two layers have left theapparatus, they are separated (i.e. after being in contact for a fewseconds). A negative of the original is seen on the exposed layer. Thelayer is then rinsed for a short period and dried.

Example 2 The same light-sensitive layer as in Example 1 is used andthis is treated with a developer having the following composition:

1000 cc. of water 5 g. of Amidol (diarninophenol hydrochloride) g. ofanhydrous sodium sulphite.

The processing is as set out in Example 1.

Example 3 The same light-sensitive layer as in Example 1 is used 0 andthe processing is carried out as follows.

The layer is dipped after exposure for a short time into a solutionwhich is prepared as follows.

A solution of 50 g. of sodium thiosulphate in water has added theretosuch a quantity of silver chloride that a solution saturated with silverchloride is formed. The layer is thereafter introduced into thefollowing developer:

1000 cc. of water 15 g. of hydroquinone 0.5 g. ofl-phenyl-3-pyrazolidone 10 g. of caustic soda 30 g. of anhydrous sodiumsulphite 0.5 g. of potassium bromide.

Temperature of developer solution: 22 C. Developing time: /2 to 2minutes.

Example 4 0.5 g. of citric acid, 0.3 of sodium chloride and 0.8 g. ofsilver nitrate, dissolved in water, are added to 1 liter of a 6 percentaqueous gelatin solution. The emulsion is left to stand for about 1 hourat 40 C., and then there are added about mg. ofl,1'-diethylbenzthiomesoethyl carbocyanine iodide (optical sensitizer)as well as 10 g. of 1,2-dihydroxy-3-cyclohexyl benzene (silver halidedeveloper substance), dissolved in water.

After casting, the layer obtained is developed in the followingsolution:

A 5 percent sodium thiosulphate solution saturated with silver chlorideis prepared as indicated in Example 3 and this solution has addedthereto, per liter, 20 g. of anhydrous sodium sulphite and 10 g. ofcaustic soda.

Example 5 0.3 g. of silver nitrate is added to 1 liter of 6 percentgelatin solution and the solution is left to stand in a thin layerexposed to light for several days. Photolytic silver is formed. 3 g. ofo-nitrobenzyl pyridinium chloride are added to this solution in the darkand the solution is cast. When exposed behind a yellow filter andprocessed as set out in Example 1, these layers produce a directpositive of the copied original.

What is claimed is:

1. A process for producing a negative photographic silver image whichconsists essentially of exposing to an object to be reproduced aphotosensitive silver halide emulsion layer of essentially uniformthickness which contains uniformly distributed throughout the layer asilver halide in an amount equivalent at most to 0.1 gram of silver persquare meter of the emulsion layer that had been cast from an emulsioncontaining a silver halide in an amount equivalent to between 0.01 and1.0 gram of silver per liter which had been prepared by adding to asolution of a Water-soluble silver salt a solution of an alkali-metalhalide in an amount between one and two stoichiometrical equivalents ofthe silver salt, so that no Ostwald ripening occurs, and subsequentlysubjecting the exposed silver halide emulsion layer to physicaldevelopment without prior fixation of the exposed silver halide emulsionlayer.

2. A process for producing a negative photographic silver image whichconsists essentially of exposing to an object to be reproduced aphotosensitive silver halide emulsion layer of essentially uniformthickness which contains uniformly distributed throughout the layer asilver halide in an amount equivalent at most to 0.1 gram. of silver persquare meter of the emulsion layer that had been cast from an emulsioncontaining a silver halide in an amount equivalent to between 0.01 and1.0 gram of silver per liter which had been prepared by adding to asolution of a water-soluble silver salt a solution of an alkali-metalhalide in an amount between one and two stoichiometrical equivalents ofthe silver salt, so that no Ostwald ripening occurs, and subsequentlywithout prior fixation of the exposed silver halide emulsion layerphysically developing the exposed silver halide emulsion layer incontact with an unexposed silver halide emulsion layer containing asilver halide of the group consisting of silver chloride and silverchlorobromide in a solution containing a silver halide solvent which iscapable of forming a soluble complex with silver halides, in whichphysical development treatment silver halide from the unexposed silverhalide layer is dissolved in the solution containing the silver halidesolvent and is deposited onto the exposed silver halide emulsion layer.

3. A process as defined in claim 2 in which the silver halide solvent isa substance of the group consisting of sodium thiosulfate and sodiumsulfite.

4. A process for producing a negative photographic silver image whichconsists essentially of exposing to an object to be reproduced aphotosensitive silver halide emulsion layer of essentially uniformthickness which contains uniformly distributed throughout the layer asilver halide in an amount equivalent at most to 0.1 gram of silver persquare meter of the emulsion layer that had been cast from an emulsioncontaining a conventional silver halide developing substance and asilver halide in an amount equivalent to between 0.01 and 1.0 gram ofsilver per liter which had been prepared by adding to a solution of awater-soluble silver salt a solution of an alkali-metal halide in anamount between one and two stoichiometrical equivalents of the silversalt, so that no Ostwald ripening occurs, and subsequently without priorfixation of the exposed silver halide emulsion layer subjecting theexposed silver halide emulsion layer to a physical development treatmentin an aqueous alkaline solution of a silver halide in a silver halidesolvent which is capable of forming a soluble complex with silverhalides.

5. A process for producing a negative photographic silver image whichconsists essentially of exposing through a yellow filter to an object tobe reproduced that is illuminated with light rays which include thegreen region of the visible spectrum a photosensitive photographicmaterial comprising (a) a silver halide emulsion as defined in claim 1that is sensitive to green light, and

(b) a silver chloride emulsion layer that is essentially sensitive onlyto blue light,

and subjecting the thus exposed photographic material without priorfixation to physical development in a solution containing a silverhalide solvent which is capable of forming a soluble complex with silverhalides, in which physical development treatment silver halide from thesilver chloride emulsion layer that was unaffected in the originalexposure is dissolved in the solution containing the silver halidesolvent and is deposited onto the exposed silver halide emulsion layer.

6. In a process for producing a direct positive silver image whichcomprises exposing an ordinary fogged photosensitive silver halideemulsion layer containing a substance that is capable of promoting theHerschel efiect to an object to be reproduced that is illuminated bylight rays within the yellow to red regions of the spectrum andsubsequently developing the said exposed fogged silver halide emulsionlayer in a silver halide developing composition, the improvement whichconsists in using, in place of such an ordinary fogged silver halideemulsion layer, a photosensitive emulsion layer of essentially uniformthickness containing uniformly distributed therethrough colloidal silverthat was produced by casting an emulsion of the group consisting of (i)photosensitive silver halide emulsions containing a silver halide in anamount equivalent to between 0.01 and 1.0 gram of silver per liter whichhad been prepared by adding to a solution of a water-soluble silver salta solution of an alkali-rnetal halide in an amount between one and twostoichiometrical equivalents of the silver salt, so that no Ostwaldripening occurs, and

(ii) photosensitive emulsions containing between 2 and 10% by weight ofgelatin and an amount of a watersoluble silver salt equivalent tobetween 0.001 and 1.0 gram of silver per liter, each of which emulsionscontains a substance that is capable of promoting the Herschel effectand has been fogged by exposure to light, and, after exposure of theemulsion layer to the object to be reproduced, subjecting without priorfixation the thus exposed emulsion layer to physical development.

7. A process as defined in claim 6 in which the substance that iscapable of promoting the Herschel effect is a substance of the groupconsisting of (i) heterocyclic compounds of the benzothiazole,

quinoline, indolenine, benzotriazole, and rhodanine series, the fusedphenyl radicals of Which are substituted by at least one nitro radical,and their alkyl quaternary ammonium salts, and

(ii) six-membered heterocyclic compounds containing a ring nitrogen atomand a nitrobenzyl substituent radical, that are capable of promoting theHerschel effect.

References Cited in the file of this patent UNITED STATES PATENTS..2,712,995 Weyde July 12, 1955 2,751,295 Salminen et al June 19, 19562,937,945 Weyde May 24, 1960 OTHER REFERENCES Wall et al.: PhotographicFacts and Formulas, Am. Photo. Publ. Co. (Boston), 1947, pp. 95 and 96.

Henney and Dudley: Handbook of Photography, pages 373-374, McGraW-Hill,New York (1939).

The Photographic Journal, Section A, January 1950,

James 'et a1 June 19, 1956

1. A PROCESS FOR PRODUCING A NEGATIVE PHOTOGRAPHIC SILVER IMAGE WHICHCONSISTS ESSENTIALLY OF EXPOSING TO AN OBJECT TO BE REPRODUCED APHOTOSENSITIVE SILVER HALIDE EMULSION LAYER OF ESSENTIALLY UNIFORMTHICKNESS WHICH CONTAINS UNIFORMLY DISTRUBUTED THROUGHOUT THE LAYER ASILVER HALIDE IN AN AMOUNT EQUIVALENT AT MOST TO 0.1 GRAM OF SILVER PERSQUARE METER OF THE EMULSION LAYER THAT HAD BEEN CAST FROM AN EMULSIONCONTAINING A SILVER HALIDE IN AN AMOUNT EQUIVALENT TO BETWEEN 0.01 AND1.0 GRAM OF SILVER PER LITER WHICH HAD BEEN PREPARED BY ADDING TO ASOLUTION OF A WATER-SOLUBLE SILVER SALT A SOLUTION OF AN ALKALI-METALHALIDE IN AN AMOUNT BETWEEN ONE AND TWO STOICHIOMETRICAL EQUIVALENTS OFTHE SILVER SALT, SO THAT NO OSTWALD RIPENING OCCURS, AND SUBSEQUENTLYSUBJECTING THE EXPOSED SILVER HALIDE EMULSION LAYER TO PHYSICALDEVELOPMENT WITHOUT PRIOR FIXATION OF THE EXPOSED SILVER HALIDE EMULSIONLAYER.